artiboi21:and why is it thay you should never go in circles? i've been doing that since i've owned my first cd and i have never found a problem with that
Because the sequence of data on a CD runs in that direction. The data is laid out on such a way that it contains built-in error checking and correction. On a red-book audio CD, for example, you can lose up to successive 4000 data points in a row, and it can still reconstruct that lost data perfectly from the neighbouring points. In, fact on an audio CD, you can lose up to 12,000 successive data values and it will still be able to interpolate a value cleverly enough that you won't hear the difference. But if you lose more than the critical number of successive values, the missing data can't be reconstructed.
If you clean the disc by gently wiping from the centre to the edge then any small scratches you introduce by doing this will tend to be at right angles to the sequence of data - so you will knock out data in lots and lots of different places, but hopefully the scratch will be narrow enough that every one of those actual data points can be perfectly reconstructed from its neighbours. If you wipe around in circles then any scratches will likely knock out not only the main data points but its neighbours as well, to the point that it becomes impossible to reconstruct what is damaged.